1. Field of the Invention
The present invention relates generally to radar systems and, more particularly, to an automotive dedicated short range radar system.
2. Description of the Related Art
Dedicated short range radar systems for automotive vehicles have enjoyed increased popularity in the United States and elsewhere. Such automotive radar systems have been allotted bandwidth centered at 76.5 gigahertz in the United States by the federal government. Such automotive radar systems are used primarily, but not exclusively, in collision avoidance systems within the automotive vehicle.
Although there are different types of radar systems, many automotive radar systems utilize a continuous wave frequency modulated (CWFM) radar system. In a CWFM radar system, a transmitter transmits a microwave signal, e.g. at a center frequency of 76.5 gigahertz, so that the transmitted radio signal repeatedly sweeps between two frequencies. In the event that there is an object within the range of the vehicle, the transmitted radio frequency is reflected back as an echo towards the vehicle transmitting the radio signal.
In order to receive the echo from the transmitted signal, a horizontally steerable antenna array is also provided on the vehicle. This horizontally steerable array includes a preset number of horizontal scan positions which are horizontally angularly spaced from each other. For example, an antenna array having 16 horizontal scan positions with the first horizontal position directed to the left side of the vehicle, the central horizontal scan position directed straightforwardly of the vehicle, and the 16th horizontal scan position directed towards the right side of the vehicle. The number of horizontal scan positions, furthermore, determines the resolution of the radar system with a higher number of horizontal scan positions resulting in greater resolution.
One disadvantage of these previously known automotive radar systems, however, is that the radar system operates in a constant mode of operation which is selected or designed as a compromise between the various different types of road conditions that will be encountered by the vehicle. For example, during operation of the vehicle on a divided highway limited access roadway, also known as expressways or freeways, the most important information for the operator of the vehicle is relatively long range radar directed forwardly and towards the right side of the vehicle. Furthermore, during such operation, high resolution of the radar system is not required but the accurate measurement of speed changes between the vehicle and the forward vehicles detected by the radar system is of high importance.
Conversely, in an urban or neighborhood environment, the vehicle as well as other objects around the vehicle moves at a much slower rate so that accurate measurement of the speed difference between the vehicle and the surrounding objects is less important than on a divided highway. However, in an urban or neighborhood roadway it is important to detect objects other than vehicles, such as pedestrians, animals, bicycle riders, and the like. Consequently, a much wider range and higher resolution for the radar system is highly desirable. Furthermore, since some objects, such as pedestrians and animals, reflect a lower power density signal back to the vehicle than an automotive vehicle, it would be advantageous to increase the power of the radar system to ensure detection of such pedestrians, animals, etc.
The previously known automotive radar systems, however, do not adapt their mode of operation as a function of the type of roadway. Consequently, a compromised fixed operation of the radar system has been employed with less than optimal operating results for different operating conditions and different types of roadways.